Flue tape?

Is tape ever used to seal the seams of a WH or furnace flue? If so, is it something other than the metal tape used to seal HVAC ductwork?

I'm asking because my home's WH has a 3" single wall that is poked into a 6" single wall that comes off the furnace. The 6" goes into 6" B that goes up and out the roof. They sealed the 3"->6" connection with metal foil tape that looks pretty sloppy.

Flue connections are normally secured with screws for mechanical stability. I don't think any tapes are rated for the heat of a single wall flue. The connections do not need to be sealed, because the pressure in theory is Zero to (negative).